Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications.
Natural gas, when used in a mobile application, may be stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, typically about −100 to −162° C. The liquefied natural gas is then drawn from the tank by gravity and/or by a boost pump, and directed to a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine's engine. In some applications, the liquid fuel may be gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.
One problem associated with pumps operating at cryogenic temperatures involves heat transfer to the fuel while inside the pump. In particular, moving components of the pump create heat through friction, and this heat (as well as ambient heat and/or heat from lubrication inside the pump) can be conducted to the fuel. If the fuel absorbs too much heat while in the pump, the fuel may gasify too early, thereby disrupting desired operation of the pump and/or the engine.
One attempt to improve pumping of a cryogenic liquid is disclosed in U.S. Pat. No. 2,837,898 (the '898 patent) that issued to Ahlstrand on Jun. 10, 1958. In particular, the '898 patent discloses a swashplate type system having three pumps disposed within a container. The container is divided into a liquid chamber and a gas chamber. Connecting rods extend through a neck of the container and the gas chamber to each of the three pumps to reciprocatingly drive the pumps. A storage tank feeds liquid fuel to a bottom of the liquid chamber. The liquid chamber is connected to the gas chamber via a connecting line, and a gas return line returns vapors and/or liquid fuel from the gas chamber to a top of the storage tank. The level of liquid fuel in the gas chamber is self-adjusting, and remains above the three pumps.
While the pump of the '898 patent may reduce some heat transfer to the liquid fuel by positioning the gas chamber above the pumps, it may still be less than optimal. In particular, the '898 patent may require a large container to accommodate both of the liquid and gas chambers, which may be difficult to package in some applications and also expensive. Further, the pumps themselves may generate heat that is still conducted into the liquid.
The disclosed pump is directed to overcoming one or more of the problems set forth above.